Semiconductor devices are becoming smaller and more dense with the evolution of new technology. However, increases in circuit density produce a corresponding increase in overall increase in chip I/O (input/output) density. Chip and substrate manufacturers are therefore constantly challenged to improve the quality of their products. One way of doing this is by identifying and eliminating defects and another way is to be able to remove these defective parts without having an adverse impact on the other components. Similarly, these manufacturers are also constantly challenged to produce components that can be readily mounted and removed from an electronic part, such as a substrate. Whereas significant improvements are being made in this regard but there is more that needs to be done.
Process improvements alone are not sufficient to eliminate all the random defects which effect both yield and reliability. Historically, screening techniques have been employed to improve product failure rates to acceptable levels by culling out many of these random defects.
Additionally, within the industry, and particularly within the semiconductor industry there is also a need to make reliable electrical connections. And, therefore it is very important that these electrical interconnects be extremely reliable before they reach the end user. This reliability is also becoming important as the electrical interconnect grids are being tighter or closer.
This and other similar issues have been addressed by the semiconductor industry in a variety of ways, for example, U.S. Pat. No. 3,534,462 (Cruickshank, et al.) disclosed a method for simultaneous multiple lead bonding. A composite cylindrical lens is used to provide the necessary beam of radiant energy to simultaneously bond the leads.
U.S. Pat. No. 3,614,832 (Chance, et al.), discloses a variety of methods to make electrical connections. For example, it discloses the use of a thermo-compression bonder that penetrates a decal backing sheet and an adhesive layer depress a strip into a contact to form an electrical contact. Another method disclosed is using a heated ultrasonic tip to make the electrical connection. The use of laser in which an energy beam is focused by means of a lens system to form the electrical connection is also disclosed.
U.S. Pat. No. 4,893,742 (Bullock), discloses an ultrasonic laser soldering system, where a bonding tool having an elongated hollow capillary which is used to firmly and securely hold an end portion of a optical fiber. A laser beam is transmitted to the end of the optical fiber to secure an electrical lead to a pad on a substrate.
U.S. Pat. No. 4,970,365 (Chalco) discloses a method and apparatus for bonding components leads to pads located on a non-rigid substrate. Energy from a laser is provided along an optical fiber into the tip, such that the laser energy is reflected by and absorbed at the wall of the cavity in the tip and thereby the frontal region and frontal surface of the tip is heated. This heated tip is then used to secure an electrical lead to a pad on a substrate. Also disclosed is an ultrasonic welding apparatus or bonder that is coupled to a horn or resonator for coupling reciprocating vibratory motion from the bonder to the bonding tip having the optical fiber.
U.S. Pat. No. 5,079,070 (Chalco, et al.) discloses repair of open defects in thin film conductors. This patent utilizes the inventive lasersonic bonding apparatus of the above-mentioned U.S. Pat. No. 4,970,365, to make the repairs of the open defects in thin film conductors.
U.S. Pat. No. 5,289,632 (Chalco, et al.) discloses a bonding tip that may be pencil-like shape. An optical fiber is centrally located within the bonding tip. In order to prevent energy loss from the bottom end of the bonding tip and to create a highly-efficient laser-beam trap, a capping layer is included to provide a seal thereat. The capping layer preferably covers the entire footprint of the bottom end of the bonding tip, and can be integrally attached to or deposited on the bottom end by means already known in the prior art.
Bond reliability has greatly been improved as a result of the absence of solder and the fact that only three parameters control the bonding process. The three parameters are tip pressure, laser power and bonding time. In order to achieve bonding rates comparable to that achieved when gang bonding, a highly controllable laser heating pulse and a fast X-Y stepper such as currently in use in wire bonding applications are combined to achieve bonding rates in order of 50 to 100 milliseconds per bond.
The present invention also solves the problem of achieving reliable solderless bonds with bare-copper pads without resultant heat damage by bonding the lead to the pad using either laser energy or using a combination of laser energy and ultrasonic energy.
The apparatus and method of the present invention results in a tool or apparatus that provides a unique optical fiber tool for mounting and/or removing of components from a semiconductor module and/or substrate.
Furthermore, the present invention is very inexpensive compared to the prior known units, which require expensive complicated mechanical connectors or probes for forming electrical contacts.